I. Field
The present disclosure relates generally to communication, and more specifically to techniques for transmitting data in cellular systems.
II. Background
A cellular system is a wireless multiple-access communication system that can concurrently communicate with multiple terminals, e.g., cellular phones. A cellular system may utilize a multiple-access technique such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), or Orthogonal Frequency Division Multiple Access (OFDMA).
A cellular system often employs multiple antennas to achieve higher throughput and/or greater reliability for data transmission on the downlink to the terminals. A terminal may estimate the downlink channel response and may send feedback information to a base station. The base station may then spatially process the data transmission for the terminal based on the feedback information. For example, the base station may perform beamforming in order to steer the data transmission toward the terminal.
Spatial processing based on feedback information (e.g., beamforming) may be undesirable for several reasons. First, overhead is incurred to send the feedback information from the terminal to the base station. Second, feedback-based spatial processing for the recipient terminals may degrade the performance of other terminals communicating with other base stations. The data transmission to the recipient terminals causes interference to the other terminals, and the spatial processing based on the feedback information may result in the interference being unpredictable to these other terminals. The unpredictable fluctuation in the interference observed by these other terminals may degrade both the accuracy of their measurements of the wireless channels and the predictability of the channel properties. The reduced measurement accuracy and channel predictability degrade link adaptation for these other terminals.
There is therefore a need in the art for techniques to transmit data in cellular systems.